Early studies of the functions of the human brain used a simple method: wait for misfortune to strike-strokes, seizures, infectious diseases, lobotomies, horrendous accidents-and see how the victim coped. In many cases survival was miraculous, and observers could only marvel at the transformations that took place afterward, altering victims’ personalities. An injury to one section can leave a person unable to recognize loved ones; some brain trauma can even make you a pathological gambler, pedophile, or liar. But a few scientists realized that these injuries were an opportunity for studying brain function at its extremes. With lucid explanations and incisive wit, Sam Kean explains the brain’s secret passageways while recounting forgotten stories of common people whose struggles, resiliency, and deep humanity made modern neuroscience possible.